Process of making cellulose acetate



memes Ang.28, neat.

(, Latent UNETE STATES PATENT @FFHCE.

JOHANWES H. KESSLER, 013 WEST ORANGE, AND VIRGIL B. SEASE, 01* NEWARK, NEW JERSEY, ASSIG-NORS T E. I. DU FONT 1m NEBKOURS 8: COMPANY, 01? WILMINGTON, DELAWARE, A COBIPORATIUN 01F s PROCES OF MAKING CELLULOSE ACETATE.

Ho Drawing,

To'aZZ whom it may concern.

Be it known that we, J OHANNES M. Kass LER and VIRGIL B. SEASE, citizens of Germany and the United States, respectively,

and residents of West Orange and Newark, respectively, in the county of Essex and State of New Jersey, have invented a certain new and useful Process of Making Cellulose Acetate, of which the following is a specification.

This invention relates to processes of producing cellulose acetate, and particularly to acetylating processes which include preliminary impregnating cellulose with at least one of the organic constitutents of the ordinary acetylating solution.

In prior processes in which cellulose has been given a preliminary treatment to facilitate its acetylation, it has been customary to carry out the preliminary treatment by 1mmersing the cellulose in a bath such as a mixture of sulfuric and acetic acids, then removing the cellulose from the bath and squeezing out of the cellulose any superfluous amount of acid. I

We have now devised a process of incorporating in cellulose a known weight of acetic acid or other conditioning agent which affords advantages over the old process. Our new process may be carried out for example as follows A mass of cellulose fibre of known weight is placed under pressure in a suitable press and the liquid which is to be incorporated in the cellulose is forced therethrough, the pressure to which the cellulose is subjected being so adjusted that the cellulose will retain a desired amount of the liquid, that is, this amount of liquid will be suflicient to saturate to the cellulose. The liquid to be thus incorporated -is usually acetic acid of 98 to 100% stren h either alone or mixed with acetic anhy ride.

In practice it is found desirable when the operation is started to have the pressure a little less than that ultimately required so that the cellulose will, at an intermediate stage, contain more liquid than the predetermined amount which is to remain therein.

to The pressure on the fibre is then increased until the fibre retains only the desired amount of liquid. After shutting ofi' the Application filed Kay 1 1919. Serial Flo. 297,166.

- supply of liquid and releasing the pressure the compressed and impregnated fibre is removed from the press and fed directly into an acetylating bath.

The amount of acetic acid which the cellulose 1s made to retain may be from 30 to 250 or 300 parts and preferable 100 parts for each 100 parts of cellulose, and the amount of acetic anhydride, when the latter is used, may be from 30 to 250 parts. Ordinarily when usmg both acid and anhydride in the preliminary treatment we prefer to incorporate about 100 parts of acetic acid and about 100 parts of acetic anhydride for each 100 parts of cellulose. Either the cellulose or the acetic acid or bothshould contain such an amount of water that the impregnated cellulose will have from 1 to about 4 parts of water for each 100 parts of cellulose. .When the water is present in the cellulose, the acetylation may follow immediately after the impregnation under pressure. lithe water is not present in the cellulose at the. time of impregnation, the impregnated cellulose must stand 24 to 48 hours before it acquires the desirable reactivity. Presumably the 1 to 3% of water generally present in glacial acetic acid furnishes the water for hydration of the cellulose duringthe period of 24 to 48 hours.

The materials to be incorporated in the cellulose by a preliminar treatment should preferably not include t e acetylating cat-.

alyst, especially if sulfuric acid is used as the catalyst, since sulfuric acid if incorporated in the cellulose prior to acetylation produces hydrolysis and leads to the formation of degraded cellulose acetates, whose Eqlutions have a low viscosity and cast brittle After impregnating the cellulose in the above-described manner, the resulting mass is placed in an aceylating bath in which the amounts of reagents are preferably such as to give to the complete mixture the following composition:

100 parts cellulose.

1 to 4 parts water.

600 parts acetic acid (glacial).

250 parts acetic anhydride.

10 parts sulfuric acid.

The mixture is vigorously stirred and cooled to room temperature or lower. At to C. a clear very viscous solution Without traces of fibres is obtained in 3 or 4 hours. About 100 parts of water, 200 parts of acetic acid and about 10 parts of sulfuric acid are added, and after thorough stirring the temperature is raised to about 60 C. and maintained at about this point for 2 or 3 hours, at which time the resulting cellulose acetate will be found to be soluble in hot benzene-alcohol, commercial ethyl acetate, aqueous alcohol, and other organic solvents. The cellulose acetate is then precipitated and washed free from impurities.

By following the procedure above outlined the quantity of acetic acid or acetic anhydride employed for a given weight of cellulose is but slightly more than the quantity ultimately incorporated in the cellulose; the handling of the materials is facilitated; loss of acetic acid and acetic anhydride by evaporation is avoided; and the workmen are not subjected to obnoxious and irritating vapors as they are when carrying out the old process.

We claim:

1. The process of producing cellulose acetate which comprises forcing a liquid comprising an acetylating agent through cellulose maintained under such pressure that saturation of the cellulose is effected with substantially the amount of said liquid which it is desired to have the cellulose retain, and then subjecting the thus impregnated cellulose to acetylation.

2. The process of producing acetate which comprises forcing a li uid comprising acetic acid through cellu ose maintained under such pressure that saturationflof the cellulose is efiected with substantially the amount of said liquid which it is desired to have the cellulose retain, and then subjecting the thus impregnated cellulose to acetylation.

3. The process of producing cellulose acetate which comprises forcing a. liquid comprising acetic acid and acetic anhydride through cellulose maintained under such pressure that saturation of the cellulose is efiected with substantially the amount of said liquid which it is desired to have the cellulose retain, and then subjecting the thus impregnated cellulose to acetylation.

4. The process of producing cellulose acetate which comprises forcing a liquid comprising acetic acid through cellulose maintained under such pressure that saturation of the cellulose is effected with substantially the amount of said liquid which it is desired to have the cellulose retain, and then subjecting the thus impregnated cellulose to an acetylating bath containing acegic acid, acetic anhydride and sulfuric ac1 cellulose 5. The process which comprises forcing aeaaoa said liquid which it is desired to have the cellulose retain.

7. The process which com rises forcing aliquid comprising acetic aci and acetic an hydride through cellulose maintained under such pressure that saturation of the cellulose is effected with substantially the amount of said liquid which it is desired to have the cellulose retain.

8. The process which comprises forcing a liquid comprising an or a-nic acetylating agent through practical y dry cellulose maintained under pressure, and so regulating the pressure that each 100 parts of the cellulose will retain from about 100 to'200 parts of said liquid.

9. The process which comprises forcing a liquid comprising about equal parts of acetic acid and acetic anhydride through cellulose maintained under pressure, and so regulating the pressure that each 100 parts of the cellulose will retain from about 100 to 200 parts of said liquid.

10. The process of producing cellulose acetate which comprises forcing a liquid comprising an acetylating agent through cellulose containing from about 1 to 4% of water, said cellulose being maintained under such pressure that saturation of the cellulose is effected with substantially the amount of said first mentioned liquid which it is desired to have the cellulose retain, and then subjecting the thus impregnated cellulose to acetylation.

11. The process of producing cellulose acetate which comprises forcing a liquid comprising acetic acid through cellulose containing from about 1 to 4% of water, said cellulose being maintained under such pressure that saturation of the cellulose is effected with substantially the amount of said first mentioned liquid which it is desired to have the cellulose retain, and then subjecting the thus impregnated cellulose to acetylation.

12. The process of producing cellulose acetate whichcomprises forcing a liquid comprising acetic acid and acetic anhydride through cellulose containing from about 1 to 4% of water, said cellulose being maintained under such ressure that saturation of the cellulose is e ected with substantially the amount of said first mentioned liquid which it is desired to have the cellulose retain, and then subjecting the thus impregnated cellulose to acetylation.

aeeaeoa 13. The process which comprises forcing from about IOO to 200 parts of said first a liquid comprising about equal parts of mentioned liquid. acetic acid and acetic anhydride through eel- 1 In testimony whereof we afiix our'signaw lulose containing from about 1 to 4% of tures. 5 water, said cellulose being maintained under pressure, and so regulatin the preure that J OHANN ES M. KESSLER. each 100 parts of the co lulose will retain VIRGIL B. SEASE. 

